U.S. patent number 9,151,238 [Application Number 14/008,175] was granted by the patent office on 2015-10-06 for fault diagnosis method, fault diagnosis system, and fault diagnosis device for engine.
This patent grant is currently assigned to HONDA MOTOR CO., LTD.. The grantee listed for this patent is Masami Haishima, Hiroshi Ito, Koji Watanabe, Kensuke Yagi. Invention is credited to Masami Haishima, Hiroshi Ito, Koji Watanabe, Kensuke Yagi.
United States Patent |
9,151,238 |
Ito , et al. |
October 6, 2015 |
Fault diagnosis method, fault diagnosis system, and fault diagnosis
device for engine
Abstract
In the present fault diagnosis method and the fault diagnosis
system for an engine, an external diagnosis device: obtains
continuous data on the incidences of misfire by misfiring cylinders
from the vehicle's side with regard to the actually occurring
misfire or past incidences of misfire; detects a misfire pattern,
which is to be classified according to the presence of continuous
incidences of misfire, on the basis of the continuous data; and
narrows down a fault site in accordance with the misfire
pattern.
Inventors: |
Ito; Hiroshi (Tokyo,
JP), Haishima; Masami (Saitama, JP),
Watanabe; Koji (Asaka, JP), Yagi; Kensuke
(Fujimi, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Ito; Hiroshi
Haishima; Masami
Watanabe; Koji
Yagi; Kensuke |
Tokyo
Saitama
Asaka
Fujimi |
N/A
N/A
N/A
N/A |
JP
JP
JP
JP |
|
|
Assignee: |
HONDA MOTOR CO., LTD. (Tokyo,
JP)
|
Family
ID: |
46930437 |
Appl.
No.: |
14/008,175 |
Filed: |
February 24, 2012 |
PCT
Filed: |
February 24, 2012 |
PCT No.: |
PCT/JP2012/054515 |
371(c)(1),(2),(4) Date: |
September 27, 2013 |
PCT
Pub. No.: |
WO2012/132677 |
PCT
Pub. Date: |
October 04, 2012 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20140020655 A1 |
Jan 23, 2014 |
|
Foreign Application Priority Data
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|
|
|
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Mar 29, 2011 [JP] |
|
|
2011-071415 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01M
15/11 (20130101); F02D 41/00 (20130101); F02D
41/22 (20130101); F02D 17/02 (20130101); F02D
2200/1015 (20130101); Y02T 10/40 (20130101) |
Current International
Class: |
F02D
41/00 (20060101); G01M 15/11 (20060101); F02D
41/22 (20060101); F02D 17/02 (20060101) |
Field of
Search: |
;123/339.1,339.11,339.15,406.13,406.14,406.16,406.27,406.29,406.33
;701/101,103,111,114 ;73/114.08,114.62 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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195 40 826 |
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2 245 027 |
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03-189371 |
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Aug 1991 |
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JP |
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4-36044 |
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JP |
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05-202801 |
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JP |
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2004-019465 |
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JP |
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2005-054630 |
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JP |
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2005-146905 |
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2009-222018 |
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Oct 2009 |
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JP |
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2009-270543 |
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JP |
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2009-280082 |
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Dec 2009 |
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JP |
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2010-133419 |
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Jun 2010 |
|
JP |
|
Other References
European Search Report application No. 12765688.2 dated Oct. 10,
2014. cited by applicant .
International Search Report mailed Mar. 27, 2012, issued in
corresponding International Application No. PCT/JP2012/054515.
cited by applicant.
|
Primary Examiner: Kwon; John
Assistant Examiner: Hoang; Johnny H
Attorney, Agent or Firm: Squire Patton Boggs (US) LLP
Claims
The invention claimed is:
1. A fault diagnosing method for diagnosing an engine by tracking
down a faulty region in the event of a misfire that occurs in a
multicylinder engine having a misfire detecting function, using an
external diagnosing machine that communicates with an engine
control unit, comprising the steps of: reading a diagnostic fault
code representative of a misfiring cylinder from the engine control
unit into the external diagnosing machine; detecting misfire
patterns classified depending on whether or not successive misfires
occur in the misfiring cylinder; and tracking down faulty regions
according to the detected misfire patterns, wherein the step of
detecting the misfire patterns further comprises the steps of:
idling the engine in accordance with an instruction from the
external diagnosing machine in an attempt to repeat a misfire in
the misfiring cylinder; if a misfire is repeated in the misfiring
cylinder, detecting the repeated misfire pattern; and if a misfire
is not repeated in the misfiring cylinder, detecting the misfire
pattern based on successive data generated upon occurrence of a
misfire in the misfiring cylinder, which are stored in the engine
control unit at a time that the diagnostic fault code is
generated.
2. The fault diagnosing method for diagnosing the engine according
to claim 1, wherein the external diagnosing machine displays, as
the misfire patterns, a graph having a horizontal axis representing
time and a vertical axis representing accumulated values of number
of misfires.
3. The fault diagnosing method for diagnosing the engine according
to claim 1, wherein the step of detecting the misfire patterns
further comprises the steps of: if a misfire is not repeated in the
misfiring cylinder, operating the engine based on data of an
operating state of the engine in an attempt to repeat the operating
state of the engine, which are stored in the engine control unit at
the time that the diagnostic fault code is generated, and if a
misfire is repeated in the misfiring cylinder in this operation,
detecting the repeated misfire pattern.
4. The fault diagnosing method for diagnosing the engine according
to claim 1, further comprising the steps of: if a misfire is
repeated in the misfiring cylinder when the engine restarted in
accordance with an instruction from the external diagnosing
machine, cranking the engine to rotate a crankshaft while canceling
fuel explosion in cylinders of the engine, detecting variations in
angular velocity of the crankshaft while the engine is being
cranked, and determining a cylinder, which has variations in
angular velocity that are equal to or smaller than a predetermined
value, as a compression pressure shortage cylinder that suffers
from a shortage of compression pressure; and successively changing
air-fuel ratios of fuel supplied to the cylinders while the engine
is not under a load, and judging an air-fuel ratio failure based on
a degree of occurrence of a misfire in the cylinders, thereby
further tracking down faulty regions.
5. The fault diagnosing method for diagnosing the engine according
to claim 1, wherein the misfire patterns represent successive
misfires in a single cylinder, successive misfires in plural
cylinders, random misfires in a single cylinder, and random
misfires in plural cylinders.
6. A fault diagnosing system for diagnosing an engine, comprising:
an engine control unit for detecting a misfire occurring in an
engine having a plurality of cylinders and storing a diagnostic
fault code representative of a misfiring cylinder; and an external
diagnosing machine for tracking down faulty regions responsible for
the misfire; wherein the external diagnosing machine acquires the
diagnostic fault code from the engine control unit and provides
guidance concerning a diagnostic work technique that depends on the
diagnostic fault code; and the external diagnosing machine detects
misfire patterns classified depending on whether or not successive
misfires occur in the misfiring cylinder, and tracks down and
displays faulty regions according to the detected misfire patterns,
and wherein when the external diagnosing machine detects a misfire
pattern, the external diagnosing machine idles the engine in an
attempt to repeat a misfire in the misfiring cylinder, if a misfire
is repeated in the misfiring cylinder, the external diagnosing
machine detects the repeated misfire pattern, and if a misfire is
not repeated in the misfiring cylinder, the external diagnosing
machine detects the misfire pattern based on successive data
generated upon occurrence of a misfire in the misfiring cylinder,
which are stored in the engine control unit at a time that the
diagnostic fault code is generated.
7. The fault diagnosing system for diagnosing the engine according
to claim 6, wherein, as the misfire patterns, the external
diagnosing machine displays a graph having a horizontal axis
representing time and a vertical axis representing accumulated
values of number of misfires.
8. The fault diagnosing system for diagnosing the engine according
to claim 6, wherein when the external diagnosing machine detects a
misfire pattern, if a misfire is not repeated in the misfiring
cylinder, the external diagnosing machine operates the engine based
on data of an operating state of the engine in an attempt to repeat
the operating state of the engine, which are stored in the engine
control unit at the time that the diagnostic fault code is
generated, and if a misfire is repeated in the misfiring cylinder
in this operation, the external diagnosing machine detects the
repeated misfire pattern.
9. The fault diagnosing system for diagnosing the engine according
to claim 6, wherein: if a misfire is repeated in the misfiring
cylinder when the engine is restarted, the external diagnosing
machine cranks the engine to rotate a crankshaft while canceling
fuel explosion in cylinders of the engine, detects variations in
angular velocity of the crankshaft while the engine is being
cranked, and determines a cylinder, which has variations in angular
velocity that are equal to or smaller than a predetermined value,
as a compression pressure shortage cylinder that suffers from a
shortage of compression pressure; and the external diagnosing
machine successively changes air-fuel ratios of fuel supplied to
the cylinders while the engine is not under a load, and judges an
air-fuel ratio failure based on a degree of occurrence of a misfire
in the cylinders, thereby further tracking down faulty regions.
10. The fault diagnosing system for diagnosing the engine according
to claim 6, wherein the misfire patterns represent successive
misfires in a single cylinder, successive misfires in plural
cylinders, random misfires in a single cylinder, and random
misfires in plural cylinders.
11. A fault diagnosing machine for diagnosing an engine having a
plurality of cylinders by tracking down faulty regions responsible
for a misfire that occurs in the engine, wherein successive data
upon occurrence of a misfire in a misfiring cylinder are acquired
directly or indirectly from a vehicle, misfire patterns, which are
classified depending on whether or not successive misfires occurs
in the misfiring cylinder, are detected based on the successive
data, and faulty regions are tracked down according to the detected
misfire patterns, and wherein when a misfire pattern is detected,
the engine is idled in an attempt to repeat a misfire in the
misfiring cylinder, if a misfire is repeated in the misfiring
cylinder, the repeated misfire pattern is detected, and if a
misfire is not repeated in the misfiring cylinder, the misfire
pattern is detected based on the successive data generated upon
occurrence of a misfire in the misfiring cylinder, which are stored
in the engine control unit at a time that the diagnostic fault code
is generated.
Description
TECHNICAL FIELD
The present invention relates to a fault diagnosing method, a fault
diagnosing system, and a fault diagnosing machine (device) for
engines, which track down a possible faulty region in the event of
a misfire occurring in a multicylinder engine that includes a
misfire detecting function.
BACKGROUND ART
There has been proposed a diagnostic apparatus for conducting a
test to track down a faulty region in a misfiring engine. See,
Japanese Laid-Open Patent Publication No. 05-202801 (hereinafter
referred to as "JP05-202801A"''). According to JP05-202801A, the
diagnostic apparatus detects an air-fuel ratio in a given cylinder,
approximately at a time when fuel stops being injected into the
cylinder, and determines which one of a fuel injection system and
an ignition system is responsible for a misfire in the cylinder
based on the detected air-fuel ratio (Abstract). More specifically,
according to JP05-202801A, if the fuel injection system is
responsible for a misfire and fuel is not properly injected, then
the air-fuel ratio remains essentially unchanged approximately at
the time that fuel stops being injected into the cylinder. However,
if the ignition system is responsible for a misfire and fuel is
injected, then the air-fuel ratio changes approximately at the time
that fuel stops being injected into the cylinder. Based on such a
finding, the diagnostic apparatus can determine which one of the
fuel injection system and the ignition system is suffering from a
fault (see paragraph "0009").
SUMMARY OF INVENTION
A test for confirming operational states of various parts (function
test), as disclosed in JP05-202801A, is highly tedious and
time-consuming and hence is of poor efficiency, because the test
needs to be conducted on each region that may possibly be
responsible for a misfire. In addition, in actuality, such a test
tends to make it difficult to perform a diagnosis if the misfire is
not repeated or is difficult to repeat.
The present invention has been made in view of the above problems.
It is an object of the present invention to provide a fault
diagnosing method, a fault diagnosing system, and a fault
diagnosing machine for engines, which are capable of greatly
reducing the number of man-hours required to identify or confirm a
faulty region responsible for a misfire.
According to the present invention, there is provided a fault
diagnosing method for diagnosing an engine by tracking down a
faulty region in the event of a misfire that occurs in a
multicylinder engine having a misfire detecting function, using an
external diagnosing machine that communicates with an engine
control unit, comprising the steps of reading a diagnostic fault
code representative of a misfiring cylinder from the engine control
unit into the external diagnosing machine, detecting misfire
patterns classified depending on whether or not successive misfires
occur in the misfiring cylinder, and tracking down faulty regions
according to the detected misfire patterns.
According to the present invention, a misfire pattern of misfires,
which are occurring at present or have occurred in the past, is
detected, and a faulty region is tracked down according to the
detected misfire pattern. Consequently, it is possible to
significantly reduce the number of man-hours required to identify
or confirm a faulty region.
The external diagnosing machine may display, as the misfire
patterns, a graph having a horizontal axis representing time and a
vertical axis representing accumulated values of number of
misfires. Therefore, the operator can easily identify a misfire
pattern by visually confirming the graph. Hence, the operator can
easily grasp the situation in relation to misfires that actually
are occurring, and classify the misfires as successive misfires or
not. Further, the operator can easily grasp an actual diagnostic
work technique in relation to judging whether or not successive
misfires are occurring, and the result of the diagnostic work
technique used to indicate whether or not successive misfires are
occurring. Accordingly, the operator can perform work with
increased efficiency. In addition, the external diagnosing machine
provides a high learning capability for improving the skills of
inexperienced operators.
The step of detecting the misfire patterns may comprise the steps
of restarting the engine in accordance with an instruction from the
external diagnosing machine in an attempt to repeat a misfire in
the misfiring cylinder, and if a misfire is not repeated in the
misfiring cylinder, detecting the misfire pattern based on
successive data generated upon occurrence of a misfire in the
misfiring cylinder, which are stored in the engine control unit at
a time that the diagnostic fault code is generated. Therefore, even
if a misfire is not repeated upon restarting the engine, it is
possible to track down faulty regions by using successive data
generated upon occurrence of a misfire at a time that the
diagnostic fault code is generated.
The step of detecting misfire patterns may comprise the steps of
idling the engine in accordance with an instruction from the
external diagnosing machine in an attempt to repeat a misfire in
the misfiring cylinder, and if a misfire is not repeated in the
misfiring cylinder, detecting the misfire pattern by causing a
misfire to occur again in the misfiring cylinder by repeating an
operating state of the engine, which is stored in the engine
control unit at a time that the diagnostic fault code is generated.
Therefore, even if it is difficult to repeat a misfire while the
engine is idling, it is possible to track down faulty regions by
positively causing a misfiring state to occur again.
The fault diagnosing method may further comprise the steps of, if a
misfire is repeated in the misfiring cylinder when the engine is
restarted in accordance with an instruction from the external
diagnosing machine, cranking the engine to rotate a crankshaft
while canceling fuel explosion in cylinders of the engine,
detecting variations in angular velocity of the crankshaft while
the engine is being cranked, and determining a cylinder, which has
variations in angular velocity that are equal to or smaller than a
predetermined value, as a compression pressure shortage cylinder
that suffers from a shortage of compression pressure, and
successively changing air-fuel ratios of fuel supplied to the
cylinders while the engine is not under a load, and judging an
air-fuel ratio failure based on a degree of occurrence of a misfire
in the cylinders, thereby further tracking down faulty regions.
Accordingly, it is possible, from among faulty regions that have
already been tracked down based on the misfire pattern, to further
track down significantly limited faulty regions, by determining a
compression pressure shortage cylinder and an air-fuel ratio
failure. Consequently, it is possible to further reduce the number
of man-hours required to identify or confirm a faulty region.
The misfire patterns may represent successive misfires in a single
cylinder, successive misfires in plural cylinders, random misfires
in a single cylinder, and random misfires in plural cylinders.
Therefore, it is possible to easily classify the misfire patterns
and to efficiently track down a faulty region.
According to the present invention, there also is provided a fault
diagnosing system for diagnosing an engine, comprising an engine
control unit for detecting a misfire occurring in an engine having
a plurality of cylinders and storing a diagnostic fault code
representative of a misfiring cylinder, and an external diagnosing
machine for tracking down faulty regions responsible for the
misfire, wherein the external diagnosing machine acquires the
diagnostic fault code from the engine control unit and provides
guidance concerning a diagnostic work technique that depends on the
diagnostic fault code, and the external diagnosing machine detects
misfire patterns classified depending on whether or not successive
misfires occur in the misfiring cylinder, and tracks down and
displays faulty regions according to the detected misfire
patterns.
According to the present invention, there is further provided a
fault diagnosing machine for diagnosing an engine having a
plurality of cylinders by tracking down faulty regions responsible
for a misfire that occurs in the engine, wherein successive data
upon occurrence of a misfire in a misfiring cylinder are acquired
directly or indirectly from a vehicle, misfire patterns, which are
classified depending on whether or not successive misfires occurs
in the misfiring cylinder, are detected based on the successive
data, and faulty regions are tracked down according to the detected
misfire patterns.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a block diagram showing a general configuration of a
fault diagnosing system according to an embodiment of the present
invention;
FIG. 2 is a view showing a general internal structure of an
engine;
FIG. 3 is a flowchart of a processing sequence, which is carried
out when a misfire occurs in the engine while a vehicle powered by
an engine is traveling normally (while the engine is operating
normally);
FIG. 4 is a first flowchart of a processing sequence for diagnosing
the engine in the event of a misfire;
FIG. 5 is a second flowchart of a processing sequence for
diagnosing the engine in the event of a misfire;
FIG. 6 is a view showing positions of areas of a work guidance
screen displayed upon diagnosis of the engine;
FIG. 7 is a diagram showing by way of example an overall work
flowchart, which is displayed in an overall work display area;
FIG. 8 is a diagram showing by way of example a plurality of
misfire patterns with corresponding misfire details, and possible
faulty regions displayed in a specific work display area;
FIG. 9 is a diagram showing by way of example test results and
possible faulty regions displayed in the specific work display
area;
FIG. 10 is a diagram showing by way of example a relationship
between strokes of a piston in each cylinder, and the magnitude of
a load applied to the crankshaft as the piston operates during
cranking of the engine, when the cylinder is operating normally,
and when the cylinder suffers from a shortage of compression
pressure;
FIG. 11 is a diagram showing by way of example a relationship
between crankshaft angles and crankshaft angular velocities,
together with strokes (intake, compression, power, and exhaust
strokes) of cylinders when first through fourth cylinders are
operating normally, and when the first cylinder suffers from a
misfire during cranking of the engine;
FIG. 12 is a diagram showing a relationship between the crankshaft
angles and the angular velocity variations shown in FIG. 11,
together with power strokes of the cylinders;
FIG. 13 is a diagram showing by way of example individual average
values of angular velocity variations in the case that a tappet
clearance of the first cylinder is normal, in the case that a
deviation of the tappet clearance is small, in the case that a
deviation of the tappet clearance is large, and in the case that
the compression pressure is zero at a time that the first cylinder
is abnormal and the second through fourth cylinders are normal;
FIG. 14 is a diagram showing ratios of the individual average
values to a total average value, based on the individual average
values of the cylinders shown in FIG. 13;
FIG. 15 is a diagram showing at an enlarged scale a portion of the
ratios shown in FIG. 14; and
FIG. 16 is a timing chart showing a relationship between engine
rotational speed, air-fuel ratios of respective cylinders, and
accumulated values of number of misfires occurring in the
respective cylinders at a time that an air-fuel ratio failure
diagnostic test is conducted.
DESCRIPTION OF EMBODIMENTS
A. Embodiment
1. Arrangement
(1) Overall Configuration
FIG. 1 is a block diagram showing the general configuration of an
engine diagnosing system 10 (hereinafter referred to simply as a
"system 10") according to an embodiment of the present invention.
The system 10 includes a vehicle 12, which incorporates an engine
16 as a target to be diagnosed, and an external diagnosing machine
14 (hereinafter also referred to as a "diagnosing machine 14") for
diagnosing the engine 16.
(2) Vehicle 12
(a) Overall Configuration
The vehicle 12 includes, in addition to the engine 16, an exhaust
gas filter 18 (hereinafter also referred to as a "filter 18") for
purifying exhaust gases emitted from the engine 16, an engine
electronic control unit 20 (hereinafter referred to as an "engine
ECU 20" or an "ECU 20") for controlling operation of the engine 16,
an ignition switch 22 (hereinafter referred to by "IGSW 22"), an
accelerator pedal 24, a depressed angle sensor 26 for detecting a
depressed angle Bap of the accelerator pedal 24, and a warning lamp
28.
(b) Engine 16
FIG. 2 shows a general internal structure of the engine 16. As
shown in FIG. 2, the engine 16 comprises a so-called in-line
four-cylinder engine having an amount-of-intake-air sensor 30, a
throttle valve 32, a degree-of-opening sensor 34, first through
fourth cylinders 36a through 36d (hereinafter referred to
collectively as "cylinders 36"), intake valves 38, exhaust valves
40, fuel injection valves 42, spark plugs 44, an air-fuel-ratio
sensor 46, a crankshaft 48, pistons 50, a starter motor 52, a
crankshaft angle sensor 54, top-dead-center sensors 56, and a
temperature sensor 58. The intake valves 38, the exhaust valves 40,
and the spark plugs 44 are disposed in facing relation to
combustion chambers 60 of the cylinders 36a through 36d.
The amount-of-intake-air sensor 30 detects an amount of air
(hereinafter referred to as "an amount of intake air Qaf") that is
drawn into the engine 16 depending on a degree of opening .theta.th
[.degree.] of the throttle valve 32, and outputs the detected
amount of intake air Qaf to the engine ECU 20. The throttle valve
32 is disposed in an intake manifold 62. The degree-of-opening
sensor 34 detects the degree of opening .theta.th of the throttle
valve 32, and outputs the detected degree of opening .theta.th to
the engine ECU 20. The fuel injection valves 42 and the spark plugs
44 are disposed in facing relation to the combustion chambers 60 of
the cylinders 36a through 36d. The air-fuel-ratio sensor 46, which
includes a non-illustrated oxygen sensor, is disposed in an exhaust
manifold 64. The air-fuel-ratio sensor 46 detects an air-fuel ratio
(hereinafter referred to as a "total air-fuel ratio Raf_total") of
the engine 16 in its entirety, and outputs the detected total
air-fuel ratio Raf_total to the engine ECU 20.
The starter motor 52 actuates the crankshaft 48 based on electric
power supplied from a battery, not shown. The crankshaft angle
sensor 54 detects a rotational angle (hereinafter referred to as a
"crankshaft angle Ac") [.degree.] of the crankshaft 48, and outputs
the detected crankshaft angle Ac to the engine ECU 20. Each of the
top-dead-center sensors 56 detects a top dead center position of a
corresponding piston 50, and outputs the detected top dead center
position to the engine ECU 20. The temperature sensor 58 detects a
temperature Tw [.degree. C.] of an engine coolant, not shown, and
outputs the detected temperature Tw to the engine ECU 20. The
temperature sensor 58 may detect the temperature To [.degree. C.]
of an engine oil, not shown.
(c) Exhaust Gas Filter 18
The exhaust gas filter 18, which is disposed downstream (on the
exhaust side) from the exhaust manifold 64, purifies exhaust gases
from the engine 16 and discharges the purified exhaust gases.
According to the present embodiment, the exhaust gas filter 18
includes a three-way catalyst for purifying exhaust gases.
(d) Engine ECU 20
The engine ECU 20 serves to control operations of the engine 16. As
shown in FIG. 1, the engine ECU 20 has an input/output unit 70, a
processor 72, and a memory 74.
According to the present embodiment, the engine ECU 20 includes and
carries out an engine rotational speed calculating function, a
misfire counting function, a throttle valve controlling function, a
fuel injection valve controlling function, and a spark plug
controlling function, for example.
The engine rotational speed calculating function is a function to
calculate a rotational speed (engine rotational speed NE) [rpm] of
the engine 16 based on output signals from the top-dead-center
sensors 56. According to the present embodiment, the engine
rotational speed calculating function is combined with the
top-dead-center sensors 56 in order to provide an engine rotational
speed sensor. Alternatively, an engine rotational speed sensor may
be provided independently of the engine ECU 20, and an output
signal from the engine rotational speed sensor may be sent to the
engine ECU 20.
The misfire counting function is a function to judge whether or not
a misfire is occurring in each of the cylinders 36a through 36d
based on output signals from the crankshaft angle sensor 54, and to
count misfires that have been judged as occurring in each of the
cylinders 36a through 36d. According to the present embodiment, the
misfire counting function is combined with the crankshaft angle
sensor 54 in order to provide a misfire counter. A misfire may be
judged as occurring by known means. For example, a combustion
pressure at a given crankshaft angle may be detected, and a misfire
may be judged as occurring if the detected combustion pressure is
equal to or lower than a predetermined value. Alternatively, a
misfire may be judged as occurring if a combustion pressure at a
given crankshaft angle is equal to or lower than a predetermined
value.
The throttle valve controlling function is a function to control
the output power of the engine 16 by controlling a degree of
opening .theta.th of the throttle valve 32, based on the depressed
angle .theta.ap of the accelerator pedal 24 or the like.
The fuel injection controlling function is a function to control
the output power of the engine 16 by controlling an injected amount
of fuel Qfi (target value) from the fuel injection valve 42 based
on the depressed angle .theta.ap of the accelerator pedal 24 or the
like.
The spark plug controlling function is a function to control the
output power of the engine 16 by controlling an ignition timing of
each of the spark plugs 44 based on the depressed angle .theta.ap
of the accelerator pedal 24 or the like.
(3) External Diagnosing Machine 14
The external diagnosing machine 14 serves to diagnose the engine 16
for faults. As shown in FIG. 1, the external diagnosing machine 14
includes a cable 82, which is connected to the engine ECU 20
through a data link connector 80 on the vehicle 12 for inputting
and outputting intravehicular data, an input/output unit 84 to
which the cable 82 is connected, an operating unit 86 in the form
of a keyboard, a touch pad, etc., not shown, a processor 88 for
controlling various components and judging each of the cylinders
36a through 36d for a malfunction, a memory 90 for storing various
data together with various programs including a control program
used by the processor 88 and a fault diagnosing program, and a
display unit 92 for displaying various items of information.
The external diagnosing machine 14 may be made up of hardware in
the form of a commercially available laptop computer, a tablet
computer, or a smartphone, for example.
For diagnosing the respective cylinders 36a through 36d for faults
using the external diagnosing machine 14, an operator (user)
connects one end of the cable 82 to the input/output unit 84 and
the other end of the cable 82 to the data link connector 80, which
is mounted on an instrument panel, not shown, of the vehicle 12.
Thereafter, the operator operates the operating unit 86 in order to
instruct the external diagnosing machine 14 to diagnose the
respective cylinders 36a through 36d for faults. The external
diagnosing machine 14 causes the engine ECU 20 to operate the
engine 16. Details of a process, which is carried out by the
external diagnosing machine 14 in order to diagnose the respective
cylinders 36a through 36d for faults, will be described later.
2. Diagnosis Upon the Occurrence of a Misfire
(1) Processing Sequence Carried Out When a Misfire Occurs
FIG. 3 is a flowchart of a processing sequence, which is carried
out when a misfire occurs in the engine 16 while the vehicle 12 is
traveling normally (while the engine 16 is operating normally). In
step S1, the engine ECU 20 detects, by way of the misfire counter,
a misfire that occurs in the engine 16.
In step S2, the engine ECU 20 stores in the memory 74 a diagnostic
fault code representative of the occurrence of a misfire, and one
of the cylinders 36a through 36d that has suffered from the
misfire. For example, if a misfire has occurred in the first
cylinder 36a, then the engine ECU 20 stores a diagnostic fault code
"P0301" in the memory 74. If a misfire has occurred in the second
cylinder 36b, then the engine ECU 20 stores a diagnostic fault code
"P0302" in the memory 74. If a misfire has occurred in the third
cylinder 36c, then the engine ECU 20 stores a diagnostic fault code
"P0303" in the memory 74. If a misfire has occurred in the fourth
cylinder 36d, then the engine ECU 20 stores a diagnostic fault code
"P0304" in the memory 74. If multiple cylinders 36a through 36d
have misfired, then the engine ECU 20 stores a diagnostic fault
code "P0300" in the memory 74.
Data, which is available for 15 seconds immediately before the
engine ECU 20 judges that a misfire has occurred, are acquired at
intervals of 0.2 seconds as relevant data in relation to the
occurrence of a misfire. The acquired data include data
representing a vehicle speed V [km/h], an engine rotational speed
NE [rpm], a temperature Tw [.degree. C.] of the coolant of the
engine 16, a depressed angle bap of the accelerator pedal 24, and a
number of misfires that have occurred in the cylinders 36a through
36d within a predetermined period (measurement period Pm, to be
described later).
In step S3, the engine ECU 20 issues a warning by turning on the
warning lamp 28, thereby indicating to the user the occurrence of a
fault (misfire). In response to the warning, the user takes the
vehicle 12 to a repair shop or the like, for example.
(2) Processing Sequence for Diagnosing Engine 16 in the Event of a
Misfire
FIGS. 4 and 5 show first and second flowcharts, respectively, of a
processing sequence for diagnosing the engine 16 in the event of a
misfire. In step S11, an operator (technician), having confirmed
that the warning lamp 28 on the vehicle 12 is turned on, connects
the external diagnosing machine 14 to the engine ECU 20 through the
cable 82 and the data link connector 80. In step S12, the processor
88 of the external diagnosing machine 14 reads a diagnostic program
from the memory 90 in response to an action made by the operator,
and activates the diagnostic program. In step S13, the operator
carries out an operation, using the operating unit 86 of the
external diagnosing machine 14, in order to read data and a
diagnostic fault code (DTC) into the external diagnosing machine 14
upon the occurrence of a fault in the engine ECU 20.
In step S14, the external diagnosing machine 14 displays a work
guidance screen for diagnostic work, which corresponds to the read
diagnostic fault code. FIG. 6 is a view showing positions of areas
of a work guidance screen 100, which are displayed when the engine
16 is diagnosed. As shown in FIG. 6, the work guidance screen 100
primarily is made up of a toolbar area 102, an overall work display
area 104, and a specific work display area 106.
The toolbar area 102 is an area for displaying a tool bar, not
shown, including icons "SAVE", "PRINT", etc. The overall work
display area 104 is an area for displaying an overall work
flowchart 110 (see FIG. 7), which depends on the diagnostic fault
code read in step S13. The specific work display area 106 is an
area for displaying specific work details, which depend on a work
title (work item) selected in the overall work flowchart 110.
FIG. 7 shows by way of example the overall work flowchart 110
displayed in the overall work display area 104. As shown in FIG. 7,
the overall work flowchart 110 has a start box 112, first through
third work title boxes 114a through 114c (hereinafter collectively
referred to as "work title boxes 114"), a plurality of vertical
arrows 116, a plurality of horizontal arrows 118, first through
fourth check result boxes 120a through 120d (hereinafter referred
to collectively as "check result boxes 120"), first through third
skip boxes 122a through 122c (hereinafter referred to as "skip
boxes 122"), a first scroll bar 124, and a second scroll bar 126
(see FIG. 6).
The start box 112 is a field for displaying a diagnostic fault code
or symptom. According to the present embodiment, the diagnostic
fault codes include codes such as "P0300", "P0301", "P0302",
"P0303", "P0304" (indicative of the occurrence of a misfire in the
engine 16).
The work title boxes 114 are fields for displaying work titles
(work items). The work titles (work items) include a diagnostic
work item and a verifying work item. The diagnostic work item is a
work item for identifying a faulty region, and the verifying work
item is a work item for repairing or replacing the identified
faulty region. In FIG. 7, the first work title box 114a, which has
a pentagonal shape, represents an overall work item, and the second
and third work title boxes 114b, 114c, which have rectangular
shapes, represent individual work items.
The vertical arrows 116 and the horizontal arrows 118 point to work
title boxes 114a and skip boxes 122, which are proceeded to in a
subsequent step.
The check result boxes 120 are fields for displaying a check
result, i.e., "OK" (repeated or normal) or "NG" (not repeated or
abnormal). Since the check result boxes 120 have a transparent
background and a transparent frame, only the letters in the check
result boxes 120 are illustrated in FIG. 7.
The skip boxes 122 are fields for displaying a skip from one work
title box 114 to another work title box 114.
The first scroll bar 124 (FIG. 6) is a scroll bar for vertically
scrolling the overall work flowchart 110 displayed in the overall
work display area 104. If the overall work flowchart 110 cannot be
displayed in its entirety within the overall work display area 104
shown in FIG. 6, then the operator can move the first scroll bar
124 in order to vertically scroll the overall work flowchart 110,
so that the operator can see the overall work flowchart 110 in its
entirety.
The second scroll bar 126 (FIG. 6) is a scroll bar for vertically
scrolling the specific work details displayed in the specific work
display area 106. If the specific work details cannot be displayed
in their entirety within the specific work display area 106 shown
in FIG. 6, then the operator can move the second scroll bar 126 in
order to vertically scroll the specific work details (see FIG. 8,
for example), so that the operator can see the specific work
details in their entirety.
The work guidance screen 100 may have a scroll bar for horizontally
scrolling the displayed information, in addition to the first
scroll bar 124 and the second scroll bar 126, which serve to
vertically scroll the displayed information.
A work title box 114 to be handled, i.e., any work item to be dealt
with, has a frame thereof displayed in bold, so that the display of
the work title box 114 to be handled is highlighted. For example,
if the second work title box 114b ("REPEATABILITY TEST") is to be
handled, then the second work title box 114b is highlighted with
the frame thereof displayed in bold. Alternatively, if the work
guidance screen 100 is displayed in color, then the background
color of any work title box 114 may be changed from blue to orange,
for example, so that the display of the work title box 114 is
highlighted.
In step S15 of FIG. 4, the operator judges whether or not the read
diagnostic fault code represents the occurrence of a misfire. If
the diagnostic fault code does not represent the occurrence of a
misfire (S15: NO), then in step S16, the operator carries out a
diagnostic process in accordance with the diagnostic fault
code.
If the diagnostic fault code represents the occurrence of a misfire
(S15: YES), then in step S17, the external diagnosing machine 14
keeps the engine 16 idling, and conducts a misfire repeatability
test on all of the cylinders 36a through 36d. In the misfire
repeatability test of step S17, a misfire is judged as being
repeated when the warning lamp 28, which indicates the occurrence
of a misfire, is turned on while the engine 16 is idling. The
operator selects one of the skip boxes 122 from within the overall
work flowchart 110 in order to enter the result of the misfire
repeatability test. Thereafter, the external diagnosing machine 14
guides the operator to perform a work process depending on the
entered result of the misfire repeatability test. Alternatively,
rather than the operator entering the result of the misfire
repeatability test, the external diagnosing machine 14 may judge
whether or not a misfire is repeated. More specifically, the
external diagnosing machine 14 keeps the engine 16 idling while
measuring with the misfire counter an accumulated value Tmf_cyl_n
of the number of misfires that have occurred in the respective
cylinders 36a through 36d during a measurement period Pm. The
variable "n" in "Tmf_cyl_n" represents the number of a cylinder in
question. For example, "Tmf_cyl_1" represents an accumulated value
with respect to the first cylinder 36a. The external diagnosing
machine 14 judges that a misfire is repeated when the accumulated
value "Tmf_cyl_n" with respect to at least one cylinder exceeds a
given threshold value for judging the occurrence of a misfire.
If a misfire is repeated while the engine 16 is idling (S18: YES),
then control proceeds to step S22. If a misfire is not repeated
while the engine 16 is idling (S18: NO), then in step S19, the
external diagnosing machine 14 conducts a misfire repeatability
test on all of the cylinders 36a through 36d while the fault that
has occurred is being repeated. The misfire repeatability test in
step S19 is the same as the misfire repeatability test in step S17,
except that the step is performed while the fault that has occurred
is being repeated, rather than while the engine 16 is idling. More
specifically, the external diagnosing machine 14 displays, within
the specific work display area 106, a message which requests the
operator to repeat the occurrence of the fault, and to acquire data
upon occurrence of a misfire, together with the data that was read
upon the occurrence of the fault in step S13. The data upon
occurrence of the fault include data representative of a vehicle
speed V [km/h], an engine rotational speed NE [rpm], a temperature
Tw [.degree. C.] of the coolant of the engine 16, and a depressed
angle .theta.ap of the accelerator pedal 24, for example. Based on
the message and the data, which are displayed in the specific work
display area 106, the operator repeats the occurrence of the fault.
If a misfire is repeated at this time, then the warning lamp 28 is
turned on in order to indicate the occurrence of a misfire.
Depending on whether or not the warning lamp 28 is turned on, the
operator judges whether a misfire is repeated, and selects one of
the skip boxes 122 from within the overall work flowchart 110 in
order to enter the result of the misfire repeatability test.
Alternatively, in the same manner as in step S17, the external
diagnosing machine 14 may operate autonomously to judge whether or
not a misfire is repeated.
If a misfire is repeated while the fault that has occurred is
repeated (S20: YES), then control proceeds to step S22. If a
misfire is not repeated while the fault that has occurred is
repeated (S20: NO), then in step S21, the external diagnosing
machine 14 displays a list of misfire-related fault data in the
past, together with details of the misfire-related fault data in
the past selected from the list displayed on the display unit 92.
The operator can now identify a faulty region based on the
misfire-related fault data in the past. The misfire-related fault
data in the past are stored in the memory 90.
In step S22, the external diagnosing machine 14 displays misfire
patterns of the cylinders 36a through 36d on the display unit 92.
FIG. 8 is a diagram showing by way of example a plurality of
misfire patterns together with corresponding misfire details and
possible faulty regions that are displayed in the specific work
display area 106.
In FIG. 8, the misfire patterns include a misfire pattern 1 in
which a single cylinder suffers from a succession of misfires
(SINGLE CYLINDER--SUCCESSIVE MISFIRES), a misfire pattern 2 in
which a plurality of cylinders suffer from a succession of misfires
(PLURAL CYLINDERS--SUCCESSIVE MISFIRES), a misfire pattern 3 in
which a single cylinder randomly misfires (SINGLE CYLINDER--RANDOM
MISFIRES), and a misfire pattern 4 in which a plurality of
cylinders randomly misfire (PLURAL CYLINDERS--RANDOM MISFIRES).
The misfire pattern 1 (SINGLE CYLINDER--SUCCESSIVE MISFIRES) is
combined with a field "MISFIRE DETAILS (MISFIRE SYMPTOM)" which
displays a statement "MISFIRING CYLINDER MISFIRES EVERY TIME AND
MISFIRE COUNTER COUNTS UP SUCCESSIVELY (LINEARLY)" and a statement
"MISFIRE COUNTER COUNTS UP FOR ONE CYLINDER ONLY" while also
displaying a graph of the misfire pattern 1 (SINGLE
CYLINDER--SUCCESSIVE MISFIRES) the horizontal axis of which
represents time (MEASURING TIME) and the vertical axis of which
represents an accumulated value Tmf_cyl_n of the number of misfires
(MISFIRE COUNTER [COUNT]). The misfire pattern 1 also is combined
with a field "POSSIBLE FAULTY REGION" which displays "IG (ignition)
COIL", "SPARK PLUG", "COMPRESSION" (compression failure), "TAPPET
CLEARANCE" (valve clearance), and "INJECTOR", as regions that
potentially are suffering from a fault according to the misfire
pattern 1.
The misfire pattern 2 (PLURAL CYLINDERS--SUCCESSIVE MISFIRES) is
combined with a field "MISFIRE DETAILS (MISFIRE SYMPTOM)" which
displays a statement "MISFIRING CYLINDERS MISFIRE EVERY TIME AND
MISFIRE COUNTER COUNTS UP SUCCESSIVELY (LINEARLY)" and a statement
"MISFIRE COUNTER COUNTS UP FOR PLURAL CYLINDERS", and also displays
a graph of the misfire pattern 2 (PLURAL CYLINDERS--SUCCESSIVE
MISFIRES) the horizontal axis of which represents time and the
vertical axis of which represents an accumulated value Tmf_cyl_n of
the number of misfires. The misfire pattern 2 also is combined with
a field "POSSIBLE FAULTY REGION" which displays "IG COIL", "SPARK
PLUG", "COMPRESSION", "TAPPET CLEARANCE", and "INJECTOR", as
regions that potentially are suffering from a fault according to
the misfire pattern 2.
The misfire pattern 3 (SINGLE CYLINDER--RANDOM MISFIRES) is
combined with a field "MISFIRE DETAILS (MISFIRE SYMPTOM)" which
displays a statement "MISFIRING CYLINDERS MISFIRE RANDOMLY
(IRREGULARLY) AND OPERATES NORMALLY AND MISFIRE COUNTER COUNTS UP
IRREGULARLY", a statement "CYLINDER OCCASIONALLY OPERATES NORMALLY
AND MISFIRE COUNTER OCCASIONALLY COUNTS UP", and a statement
"MISFIRE COUNTER COUNTS UP FOR ONE CYLINDER ONLY", and also
displays a graph of the misfire pattern 3 (SINGLE CYLINDER--RANDOM
MISFIRES) the horizontal axis of which represents time and the
vertical axis of which represents an accumulated value Tmf_cyl_n of
the number of misfires. The misfire pattern 3 also is combined with
a field "POSSIBLE FAULTY REGION" which displays "IG COIL",
"CRANKSHAFT PULSER", "CRANKSHAFT SENSOR", "VTEC" (variable valve
timing/valve lifting mechanism), "COMPRESSION", and "TAPPET
CLEARANCE", as regions that potentially are suffering from a fault
according to the misfire pattern 3.
The misfire pattern 4 (PLURAL CYLINDERS--RANDOM MISFIRES) is
combined with a field "MISFIRE DETAILS (MISFIRE SYMPTOM)" which
displays a statement "MISFIRING CYLINDERS MISFIRE RANDOMLY
(IRREGULARLY) AND OPERATES NORMALLY AND MISFIRE COUNTER COUNTS UP
IRREGULARLY", a statement "CYLINDERS OCCASIONALLY OPERATE NORMALLY
AND MISFIRE COUNTER OCCASIONALLY COUNTS UP", and a statement
"MISFIRE COUNTER COUNTS UP FOR ALL CYLINDERS OR PLURAL CYLINDERS",
and also displays a graph of the misfire pattern 4 (PLURAL
CYLINDERS--RANDOM MISFIRES) the horizontal axis of which represents
time and the vertical axis of which represents an accumulated value
Tmf_cyl_n of the number of misfires. The misfire pattern 4 also is
combined with a field "POSSIBLE FAULTY REGION" which displays
"CRANKSHAFT PULSER", "CRANKSHAFT SENSOR", "EGR VALVE", "VTEC",
"COMPRESSION", "TAPPET CLEARANCE", "FUEL CHAMBER", "FUEL SYSTEM"
(FUEL PRESSURE, PUMP, FILTER), and "ENGINE BODY" as regions that
potentially are suffering from a fault according to the misfire
pattern 4.
The displayed information shown in FIG. 8 is used as a guideline
for the operator to judge the misfire pattern. In addition to the
displayed information shown in FIG. 8, the external diagnosing
machine 14 displays, in the specific work display area 106, graphs
(not shown, identical to those shown in FIG. 8) of the accumulated
values Tmf_cyl_n of the present number of misfires occurring in the
respective cylinders 36a through 36d. If a misfire is repeated
while the engine 16 is idling (S18: YES), then data acquired up to
that time are used as the accumulated values Tmf_cyl_n of the
present number of misfires. If a misfire is not repeated while the
engine 16 is idling (S18: NO), then data upon the occurrence of the
misfire are used as the accumulated values Tmf_cyl_n of the present
number of misfires. In addition, misfire pattern options are
displayed in the specific work display area 106.
Based on the displayed information shown in FIG. 8 and the graphs
of the accumulated values Tmf_cyl_n of the present number of
misfires, the operator selects one of the misfire pattern options
using the operating unit 86. In this manner, a misfire pattern is
selected.
In step S23 shown in FIG. 5, the external diagnosing machine 14
conducts a compression pressure failure judgment test. The
compression pressure failure judgment test is a test for judging a
compression pressure failure in the cylinders 36a through 36d, and
is capable of determining whether or not a mechanical system fault
is occurring, as will be described in detail later.
In step S24, the external diagnosing machine 14 conducts an
air-fuel-ratio failure diagnostic test. The air-fuel-ratio failure
diagnostic test is a test for diagnosing an air-fuel-ratio failure
in the cylinders 36a through 36d, and is capable of determining a
lean failure in which the air-fuel ratio is excessively low, and a
rich failure in which the air-fuel ratio is excessively high.
In step S25, the external diagnosing machine 14 tracks down regions
(hereinafter referred to as "possible faulty regions") where a
fault possibly is occurring based on the results of the misfire
repeatability test (S17, S19), the compression pressure failure
judgment test (S23), and the air-fuel-ratio failure diagnostic test
(S24), and displays the possible faulty region along with the
results of the tests.
FIG. 9 is a diagram showing by way of example test results and
possible faulty regions, which are displayed in the specific work
display area 106. In FIG. 9, the possible faulty regions are
displayed depending on the misfire patterns 1 through 4, the result
of the compression pressure failure judgment test, and the result
of the air-fuel-ratio failure diagnostic test.
More specifically, if the misfire pattern is "1" (SINGLE
CYLINDER--SUCCESSIVE MISFIRES) or "2" (PLURAL CYLINDERS--SUCCESSIVE
MISFIRES) and the result of the compression pressure failure
judgment test indicates "NOT PASSED" (mechanical fault), then
"COMPRESSION" and "TAPPET CLEARANCE (LARGE)" are displayed as
possible faulty regions. If the misfire pattern is "1" or "2", the
result of the compression pressure failure judgment test
indicates
"PASSED" (no mechanical fault), and the result of the
air-fuel-ratio failure diagnostic test indicates "LEAN FAILURE",
then "IG COIL", "SPARK PLUG", and "INJECTOR" are displayed as
possible faulty regions. If the misfire pattern is "1" or "2", the
result of the compression pressure failure judgment test indicates
"PASSED" (no mechanical fault), and the result of the
air-fuel-ratio failure diagnostic test indicates "RICH FAILURE",
then "INJECTOR" is displayed as a possible faulty region.
If the misfire pattern is "3" (SINGLE CYLINDER--RANDOM MISFIRES)
and the result of the compression pressure failure judgment test
indicates "NOT PASSED" (mechanical fault), then "COMPRESSION" and
"TAPPET CLEARANCE (LARGE)" are displayed as possible faulty
regions. If the misfire pattern is "3", the result of the
compression pressure failure judgment test indicates "PASSED" (no
mechanical fault), and the result of the air-fuel-ratio failure
diagnostic test indicates "LEAN FAILURE", then "IG COIL", "TAPPET
CLEARANCE (SMALL)", and "INJECTOR" are displayed as possible faulty
regions. If the misfire pattern is "3", the result of the
compression pressure failure judgment test indicates "PASSED", and
the result of the air-fuel-ratio failure diagnostic test indicates
"RICH FAILURE", then "INJECTOR" is displayed as a possible faulty
region. If the misfire pattern is "3", and the result of the
compression pressure failure judgment test and the result of the
air-fuel-ratio failure diagnostic test indicate "PASSED", then "IG
COIL", "CRANKSHAFT PULSER", "CRANKSHAFT SENSOR", and "VTEC" are
displayed as possible faulty regions.
If the misfire pattern is "4" (PLURAL CYLINDERS--RANDOM MISFIRES)
and the result of the compression pressure failure judgment test
indicates "NOT PASSED" (mechanical fault), then "COMPRESSION" and
"TAPPET CLEARANCE (LARGE)" are displayed as possible faulty
regions. If the misfire pattern is "4", the result of the
compression pressure failure judgment test indicates "PASSED" (no
mechanical fault), and the result of the air-fuel-ratio failure
diagnostic test indicates "LEAN FAILURE", then "TAPPET CLEARANCE
(SMALL)", "FUEL CHAMBER", "FUEL SYSTEM (FUEL PRESSURE, PUMP,
FILTER)", "EGR OPENING FAILURE", and "EGR LEAKAGE" are displayed as
possible faulty regions. If the misfire pattern is "4", the result
of the compression pressure failure judgment test indicates
"PASSED", and the result of the air-fuel-ratio failure diagnostic
test indicates "RICH FAILURE", then "INJECTOR" is displayed as a
possible faulty region. If the misfire pattern is "4", and the
result of the compression pressure failure judgment test and the
result of the air-fuel-ratio failure diagnostic test indicate
"PASSED", then "CRANKSHAFT PULSER", "CRANKSHAFT SENSOR", "VTEC
SWITCHING DELAY", and "EGR FOLLOW-UP DELAY" are displayed as
possible faulty regions.
In step S26 of FIG. 5, the operator judges a fault of each of the
possible faulty regions. For example, the specific possible faulty
regions (compression, IG coil, etc.) shown in FIG. 9 are linked
together with data concerning specific work details. The operator
enters one of the options (possible faulty regions) using the
operating unit 86. Thereafter, the external diagnosing machine 14
displays, in the specific work display area 106, an overall work
flowchart 110 depending on the entered option (possible faulty
region) in the overall work display area 104, and also displays
specific work details according to the work title box 114 selected
in the overall work flowchart 110. The operator refers to the
displayed information in order to confirm whether or not a fault
actually is occurring in the possible faulty region. If a fault is
actually occurring in the possible faulty region, then the operator
repairs the possible faulty region.
The compression pressure failure judgment test and the
air-fuel-ratio failure diagnostic test according to the present
embodiment will be described below.
(3) Compression Pressure Failure Judgment Test
As described above, the compression pressure failure judgment test
is a test for judging a compression pressure failure in the
cylinders 36a through 36d, and is capable of judging whether or not
a mechanical system fault is occurring. In the compression pressure
failure judgment test, the engine 16 is cranked to rotate the
crankshaft 48 while at the same time canceling fuel explosion in
the cylinders 36a through 36d, and those of the cylinders 36a
through 36d that are suffering from a compression pressure failure
(compression pressure failure cylinder) are judged based on an
angular velocity variation .DELTA..omega. [rad/s] of the crankshaft
48. According to the present embodiment, when the engine 16 is
cranked, both the fuel supply system (fuel injection valve 42,
etc.) and the ignition system (spark plug 44, etc.) are
disabled.
FIG. 10 is a diagram showing a model representation of a
relationship between strokes of the piston 50 in each of the
cylinders 36a through 36d and the magnitude of a load L1 applied to
the crankshaft 48 during operation of the piston 50 upon cranking
the engine, at a time that the cylinder 36 is operating normally
and when the cylinder 36 is suffering from a shortage of
compression pressure. The load L1 induces a reduction in engine
rotational speed NE [rpm], i.e., a reduction in the angular
velocity .omega. [rad/s] of the crankshaft 48. Since fuel explosion
is canceled in the cylinders 36a through 36d when the engine is
cranked, explosion of fuel does not actually occur in the power
stroke shown in FIG. 10. Stated otherwise, the power stroke shown
in FIG. 10 represents a stroke having the same range of the
crankshaft angle Ac as the power stroke during normal operation of
the engine.
In the example shown in FIG. 10, the load L1 applied when the
cylinder 36 is operating normally and the load L1 applied when the
cylinder 36 is suffering from a shortage of compression pressure
are compared with each other. The difference between the compared
loads L1 is particularly large during the compression stroke
compared with during the intake stroke, the power stroke, and the
exhaust stroke. This is because the compressive load is small when
a gas leakage occurs somewhere in the cylinder 36.
With the engine 16 having the plural cylinders 36a through 36d,
strokes of the cylinders 36a through 36d are kept out of phase with
each other in order to produce regular angular velocity variations
.DELTA..omega. which allow the engine 16 to be cranked stably
during normal operation thereof. However, when a compression
failure occurs in either one of the cylinders 36a through 36d, the
compressive load is not applied as required, thereby causing a
disturbance in angular velocity variations .DELTA..omega..
According to the present embodiment, which is based on the above
observations, the difference between the loads L1 in the
compression stroke is not used directly, but rather, angular
velocity variations .DELTA..omega. in the power stroke are used to
judge a shortage of compression pressure. More specifically, this
is based on the fact that, when the engine 16 having the cylinders
36a through 36d, which include one cylinder that suffers from a
shortage of compression pressure, is cranked, the crankshaft
angular velocity .omega. increases during the compression stroke of
the cylinder that suffers from a shortage of compression pressure,
but in reaction thereto, decreases in the next stroke, i.e., the
power stroke, of the same cylinder. It is thus possible to judge
whether or not a shortage of compression pressure has occurred
based on a reduction (variation) in the angular velocity co during
the power stroke. Accordingly, if the crankshaft angular velocity
variation .DELTA..omega. is used in the logic for judging a
misfire, then the same logic used for judging a misfire can also be
used as a logic for determining a cylinder that suffers from a
shortage of compression pressure.
FIG. 11 shows a model representation of the relationship between
crankshaft angles Ac and crankshaft angular velocities .omega.,
along with strokes (intake, compression, power, and exhaust
strokes) of the cylinders 36a through 36d when the cylinders 36a
through 36d operate normally and when the first cylinder 36a is
suffering from a misfire while the engine is being cranked. In FIG.
11, the solid-line curve 130 represents a relationship between
crankshaft angles Ac and crankshaft angular velocities .omega. at a
time that the cylinders 36a through 36d are operating normally,
whereas the broken-line curve 132 represents a relationship between
crankshaft angles Ac and crankshaft angular velocities .omega. at a
time that the first cylinder 36a is misfiring.
In the example shown in FIG. 11, the angular velocity .omega. drops
sharply due to a rotational disturbance in the power stroke, which
occurs subsequent to the compression stroke of the first cylinder
36a.
FIG. 12 shows a relationship between crankshaft angles Ac and
angular velocity variations .DELTA..omega., which correspond to the
data shown in FIG. 11 and the power strokes of the cylinders 36a
through 36d. In FIG. 12, the solid-line curve 140 represents a
relationship between crankshaft angles Ac and angular velocity
variations .DELTA..omega. at a time that the cylinders 36a through
36d are operating normally, whereas the broken-line curve 142
represents a relationship between crankshaft angles Ac and angular
velocity variations .DELTA..omega. at a time that the first
cylinder 36a is misfiring. In the example shown in FIG. 12, in
order to clearly show a compression pressure failure, compression
leakages (zero compression pressure) are shown which occur during
compression strokes of the first cylinder 36a. In the example shown
in FIG. 12, angular velocity variations .DELTA..omega. are reduced
in the power stroke of the first cylinder 36a. This is because a
compressive load is not applied while a corresponding increase
occurs in the angular velocity variation .DELTA..omega. during the
compression stroke of the first cylinder 36a, and then as a
reaction thereto, the angular velocity variation .DELTA..omega.
decreases in the power stroke of the cylinder 36a. It is thus
possible to judge whether or not a shortage of compression pressure
has occurred in the first cylinder 36a based on a comparison of
angular velocity variations .DELTA..omega. during respective power
strokes.
More specifically, the external diagnosing machine 14 calculates
individual average values AVEr, a total average value AVEt, and
ratios R1 based on the acquired angular velocity variations
.DELTA..omega.. The individual average values AVEr represent
average values of angular velocity variations .DELTA..omega. that
occur in respective power strokes of the cylinders 36a through 36d.
The total average value AVEt is an average of the individual
average values AVEr of all of the cylinders 36a through 36d. The
ratios R1 are calculated as a quotient of the individual average
values AVEr divided by the total average value AVEt
(AVEr/AVEt).
The external diagnosing machine 14 judges whether or not there is a
mechanical fault in the cylinders 36a through 36d based on the
previously read diagnostic fault code and the ratios R1, and
displays the judgment result on the display unit 92.
In particular, the external diagnosing machine 14 judges whether or
not there is a shortage of compression pressure in a misfiring
cylinder based on the ratios R1 with respect to the cylinders 36a
through 36d. More specifically, if the ratio R1 with respect to a
misfiring cylinder is smaller than a threshold value by which it is
judged whether or not there is a shortage of compression pressure
(compression force shortage judging threshold value TH2), then the
ECU 20 judges that there is a shortage of compression pressure in
the misfiring cylinder. According to the present embodiment, the
threshold value TH2 is 100%.
FIG. 13 shows by way of example individual average values AVEr in
the case that the tappet clearance TC of the first cylinder 36a is
normal (e.g., TC=0.23 mm), in the case that the deviation of the
tappet clearance deviation TC is small (e.g., TC=0.13 mm), in the
case that the deviation of the tappet clearance TC is large (e.g.,
TC=0.05 mm), and in the case that the compression pressure is zero
at a time that the first cylinder 36a is abnormal and the second
through fourth cylinders 36b through 36d are normal.
The solid-line curve 150 represents individual average values AVEr
in the case that the tappet clearance TC of the first cylinder 36a
is normal (e.g., TC=0.23 mm). The broken-line curve 152 represents
individual average values AVEr in the case that the deviation of
the tappet clearance deviation TC is small (e.g., TC=0.13 mm). The
dot-and-dash-line curve 154 represents individual average values
AVEr in the case that the deviation of the tappet clearance TC is
large (e.g., TC=0.05 mm). The two-dot-and-dash-line curve 156
represents individual average values AVEr in the case that the
compression pressure is zero.
FIG. 14 shows ratios R1 (=Avr/AVEt) of the individual average
values AVEr to the total average value AVEt, based on individual
average values AVEr of the cylinders 36a through 36d shown in FIG.
13. FIG. 15 is a diagram showing, at an enlarged scale, a portion
of the ratios shown in FIG. 14. In FIGS. 14 and 15, the solid-line
curve 160 corresponds to the first cylinder 36a, the broken-line
curve 162 corresponds to the second cylinder 36b, the
dot-and-dash-line curve 164 corresponds to the third cylinder 36c,
and the two-dot-and-dash-line curve 166 corresponds to the fourth
cylinder 36d.
According to the above process, the external diagnosing machine 14
judges a compression pressure failure of the cylinders 36a through
36d in order to determine whether or not a mechanical fault has
occurred.
(4) Air-Fuel-Ratio Failure Diagnostic Test
As described above, the air-fuel-ratio failure diagnostic test is a
test for diagnosing an air-fuel-ratio failure in the cylinders 36a
through 36d, and is capable of judging the occurrence of a lean
failure in which the air-fuel ratio is excessively low, and a rich
failure in which the air-fuel ratio is excessively high.
(a) Air-Fuel Ratio Control Process According to the Present
Embodiment
First, an air-fuel ratio control process according to the present
embodiment will be described below. According to the present
embodiment, an ordinary air-fuel ratio control process generally is
used during operation of the engine 16. The ordinary air-fuel ratio
control process is a control process, which is used in the fuel
injection valve controlling function of the engine ECU 20. Such a
process comprises a combination of a basic fuel injection control
process and an air-fuel-ratio feedback control process (hereinafter
referred to as an "air-fuel-ratio FB control process").
According to the present embodiment, the basic fuel injection
control process is a control process for bringing ratios of the air
and fuel (gasoline) in an air-fuel mixture supplied to the
cylinders 36a through 36d (hereinafter referred to as "cylinder
air-fuel ratios Raf_1 through Raf_4" or collectively as "cylinder
air-fuel ratios Raf_n" or simply "air-fuel ratios Raf_n") into a
stoichiometric air-fuel ratio (fuel:air=1:14.7).
More specifically, according to a basic fuel injection control
process, a relationship between amounts of intake air Qaf, which
are detected by the amount-of-intake-air sensor 30, and target
values for the injected amounts of fuel Qfi from the fuel injection
valves 42 are established beforehand as a map, and the fuel
injection valves 42 are controlled depending on a target value for
the injected amounts of fuel Qfi, which correspond to a detected
amount of intake air Qaf.
However, due to various factors including variations in operation
timings (tappet clearances TC) of the intake valves 38 and the
exhaust valves 40 of the cylinders 36a through 36d, as well as
aging of the fuel injection valve 42, the air-fuel ratios Raf_n of
the cylinders 36a through 36d and the total air-fuel ratio
Raf_total of the engine 16 overall may not necessarily be
equivalent to the stoichiometric air-fuel ratio.
According to the present invention, the air-fuel ratio FB control
process is a control process for equalizing the total air-fuel
ratio Raf_total to the stoichiometric air-fuel ratio under a
feedback control. More specifically, if the detected value from the
air-fuel ratio sensor 46 is not equivalent to the stoichiometric
air-fuel ratio, then injected amounts of fuel Qfi from all of the
fuel injection valves 42 are increased or reduced in order to
equalize the detected value with the stoichiometric air-fuel ratio.
At this time, the injected amounts of fuel Qfi are corrected using
a corrective value Pc. The corrective value Pc is a corrective
value for later-described fuel injection ratios Rfi_n [%] (target
values) of the cylinders 36a through 36d. However, the corrective
value Pc may be a corrective value for a different parameter, for
example, the injected amounts of fuel Qfi (target values) or the
total air-fuel ratio Raf_total.
According to the present embodiment, since only one air-fuel ratio
sensor 46 is disposed downstream of the exhaust manifold 64,
air-fuel ratios Raf_n of each of the respective cylinders 36a
through 36d are not detected. In the basic fuel injection control
process, therefore, the air-fuel ratios Raf_n of respective
cylinders 36a through 36d cannot be made to converge to the
stoichiometric air-fuel ratio, although the total air-fuel ratio
Raf_total of the engine 16 can be made to converge to the
stoichiometric air-fuel ratio.
(b) Air-Fuel-Ratio Failure Diagnostic Test
FIG. 16 is a timing chart showing a relationship between the engine
rotational speed NE, the air-fuel ratios of the respective
cylinders 36a through 36d (cylinder air-fuel ratios Raf_n), and the
accumulated values Tmf_cyl_n [counts] of the number of misfires
occurring in the respective cylinders 36a through 36d at the time
the air-fuel ratio failure diagnostic test is conducted.
In FIG. 16, the period from time t1 to time t2 defines a warming-up
period of the engine 16, the period from time t3 to time t4 defines
a test period for diagnosing the first cylinder 36a, the period
from time t4 to time t5 defines a test period for diagnosing the
second cylinder 36b, the period from time t5 to time t6 defines a
test period for diagnosing the third cylinder 36c, and the period
from time t6 to time t7 defines a test period for diagnosing the
fourth cylinder 36d.
In the air-fuel-ratio failure diagnostic test, as shown in FIG. 16,
the cylinders 36a through 36d are operated one by one while
changing the cylinder air-fuel ratios Raf_n in a stepwise manner
with respect to the cylinders 36a through 36d, which serve as
targets to be diagnosed (hereinafter referred to as "target
cylinders"). At this time, accumulated values Tmf_cyl_n are
detected. The accumulated values Tmf_cyl_n represent accumulated
values of the number of misfires of the target cylinders during a
measurement period Pm [sec]. The variable "n" in "Tmf_cyl_n" is
indicative of the number of a given cylinder in question from among
the cylinders 36a through 36d. For example, "Tmf_cyl_1" represents
an accumulated value with respect to the first cylinder 36a.
Cylinders 36a through 36d other than the target cylinder are
controlled according to the basic fuel injection control
process.
The measurement period Pm is a period for switching between
corrective values Cfi_n, i.e., a period for switching between the
fuel injection ratios Rfi_n and the cylinder air-fuel ratios Raf_n
(see FIG. 16). Therefore, the accumulated values Tmf_cyl_n
represent accumulated values of the number of misfires of the
target cylinders each time that the corrective values Cfi_n are
switched.
If the cylinder air-fuel ratios Raf_n are not abnormal, then the
accumulated values Tmf_cyl_n are zero when the cylinder air-fuel
ratios Raf_n are 0%, and the accumulated values Tmf_cyl_n increase
as the cylinder air-fuel ratios Raf_n differ progressively away
from 0%. It is possible to judge whether or not an air-fuel ratio
failure is occurring in the cylinders 36a through 36d by confirming
a relationship between the cylinder air-fuel ratios Raf_n and the
accumulated values Tmf_cyl_n for the respective cylinders 36a
through 36d. More specifically, if the accumulated values Tmf_cyl_n
of the number of misfires are smaller when the cylinder air-fuel
ratios Raf_n are negative values (e.g., -20%) than when the
cylinder air-fuel ratios Raf_n are 0%, then the cylinders 36a
through 36d can be the to be suffering from a rich failure in which
fuel is injected in an excessive rich state. If a misfire has
already occurred when the cylinder air-fuel ratios Raf_n are 0%
(e.g., the accumulated values Tmf_cyl_n of the number of misfires
are greater than a predetermined threshold value) and the
accumulated values Tmf_cyl_n of the number of misfires are greater
when the cylinder air-fuel ratios Raf_n are negative values (e.g.,
-20%), then the cylinders 36a through 36d can be the to be
suffering from a lean failure in which fuel is injected in an
excessively lean state.
Therefore, the external diagnosing machine 14 is capable of judging
whether or not the cylinders 36a through 36d are suffering from a
rich failure or a lean failure, based on the relationship between
the cylinder air-fuel ratios Raf_n and the accumulated values
Tmf_cyl_n of the number of misfires.
3. Advantages of the Present Embodiment
According to the present embodiment, as described above, a misfire
pattern of misfires which actually are occurring or that have
occurred in the past is detected, and a faulty region is tracked
down according to the detected misfire pattern (FIGS. 8 and 9).
Consequently, it is possible to significantly reduce the number of
man-hours required to identify and confirm a faulty region.
According to the present embodiment, the external diagnosing
machine 14 displays as a misfire pattern a graph having a
horizontal axis representing time and a vertical axis representing
the accumulated values Tmf_cyl_n, (see FIG. 8). Therefore, the
operator can easily identify the misfire pattern by visually
confirming the graph. The operator can thus easily grasp the
situation in relation to misfires that actually are occurring, and
to classify the misfires as successive misfires or not. The
operator can easily grasp an actual diagnostic work technique
concerning judgment of whether successive misfires are occurring or
not, and the result of the diagnostic work technique, which is
indicative of whether or not successive misfires are occurring, so
that the operator can perform work with increased efficiency. In
addition, the external diagnosing machine 14 enables even
inexperienced operators to upgrade their skill with a high learning
capability.
According to the present embodiment, the external diagnosing
machine 14 instructs restarting of the engine 16 in an attempt to
repeat a misfire in a misfiring cylinder (S17 or S19 in FIG. 4). If
a misfire is not repeated (S18: NO or S20: NO), then the external
diagnosing machine 14 detects a misfire pattern based on data that
was produced upon the occurrence of a misfire (S21). Therefore,
even if misfiring is not repeated when the engine 16 is restarted,
it is possible to track down faulty regions by using successive
data collected upon the occurrence of a misfire at the time that
the diagnostic fault code was generated.
According to the present embodiment, the external diagnosing
machine 14 instructs the engine 16 to idle in an attempt to repeat
a misfire in a misfiring cylinder (S17 in FIG. 4). If a misfire is
not repeated (S18: NO), then the external diagnosing machine 14
repeats the situation that took place upon the occurrence of a
misfire, based on data that was produced upon the occurrence of a
misfire, in order to repeat a misfire in the misfiring cylinder,
whereupon the external diagnosing machine 14 detects a misfire
pattern (S19). Therefore, even if it is difficult to repeat a
misfire while the engine 16 is idling, it is possible to track down
faulty regions by positively repeating the condition that took
place upon misfiring.
According to the present embodiment, if a misfire is repeated in a
misfiring cylinder when the external diagnosing machine 14
instructs restarting of the engine 16 (S18: YES or S20: YES), the
external diagnosing machine 14 further tracks down a faulty region
by determining a compression pressure shortage cylinder using the
compression pressure failure judgment test, and by judging an
air-fuel ratio failure using the air-fuel ratio failure diagnostic
test. Thus, by determining a compression pressure shortage cylinder
and judging an air-fuel ratio failure, it is possible to further
track down, from the faulty regions that have been tracked down
based on the misfire pattern, considerably limited faulty regions.
Consequently, it is possible to further reduce the number of
man-hours required to identify and confirm a faulty region.
According to the present embodiment, the misfire patterns include
successive misfires that take place in a single cylinder and in
plural cylinders, random misfires in a single cylinder, and random
misfires in plural cylinders (FIG. 8). Therefore, it is possible to
easily classify the misfire patterns and efficiently track down a
faulty region.
B. Modifications
The present invention is not limited to the above embodiment, but
may employ various additional or alternative arrangements based on
the above disclosure of the present invention. For example, the
present invention may employ the following arrangements.
1. External Diagnosing Machine 14
In the above embodiment, the external diagnosing machine 14 is used
to diagnose the engine 16 of the vehicle 12. However, the external
diagnosing machine 14 may be used in connection with other systems
having internal combustion engines, e.g., mobile objects such as
ships or the like. In the above embodiment, the external diagnosing
machine 14 communicates with the engine ECU 20 from an external
location outside of the vehicle 12. However, the external
diagnosing machine 14 may be incorporated in the vehicle 12. Stated
otherwise, the engine ECU 20 may include the functions of the
external diagnosing machine 14.
2. Engine 16
In the above embodiment, the engine 16 is an in-line four-cylinder
engine. However, the layout and number of the cylinders 36 are not
limited to those that make up parts of an in-line four-cylinder
engine. The engine 16 may be a V-shaped six-cylinder engine. If the
engine 16 is a V-shaped six-cylinder engine, the strokes, i.e., the
intake, compression, power, and exhaust strokes, of the six
cylinders occur successively in two revolutions (720.degree.) of
the crankshaft 48. Consequently, crankshaft angles Ac, which are
incremented by 120.degree. (=720.degree./6), are assigned
respectively to the power strokes of the cylinders.
3. Air-Fuel Ratio Sensor 46
In the above embodiment, the engine 16 in its entirety has one
air-fuel ratio sensor 46. However, plural air-fuel ratio sensors 46
may be combined with the respective cylinders 36.
4. Misfire Repeatability Test
In the above embodiment, two types of misfire repeatability tests
(while the engine is idling, and during repetition of a situation
upon occurrence of a misfire) are conducted. However, either one of
these two types of misfire repeatability tests may be
conducted.
In the above embodiment, the misfire patterns include "SINGLE
CYLINDER--SUCCESSIVE MISFIRES", "PLURAL CYLINDERS--SUCCESSIVE
MISFIRES", "SINGLE CYLINDER--RANDOM MISFIRES", and "PLURAL
CYLINDERS--RANDOM MISFIRES". However, the misfire patterns may
include two types of misfire patterns, e.g., "SUCCESSIVE MISFIRES"
and "RANDOM MISFIRES", or three types of random misfires, e.g.,
"SUCCESSIVE MISFIRES", "SINGLE CYLINDER--RANDOM MISFIRES", and
"PLURAL CYLINDERS--RANDOM MISFIRES".
In the above embodiment, the operator judges misfire patterns.
However, the external diagnosing machine 14 may judge misfire
patterns automatically. If the external diagnosing machine 14
automatically judges misfire patterns, then a first misfire
threshold value for distinguishing between the absence of a misfire
and random misfires, and a second misfire threshold value for
distinguishing between random misfires and successive misfires may
be established in advance. In this case, the external diagnosing
machine 14 compares the accumulated value Tmf_cyl_n of the number
of misfires with respect to the cylinders 36a through 36d with the
first misfire threshold value and the second misfire threshold
value, thereby judging whether each of the cylinders 36a through
36d is not suffering from a misfire, or suffers from random or
successive misfires.
In the above embodiment, both the displayed information shown in
FIG. 8 and the graph of the accumulated values Tmf_cyl_n of the
present number of misfires are displayed in the specific work
display area 106, as guidelines for enabling the operator to judge
a misfire pattern. However, only the accumulated values Tmf_cyl_n
of the present number of misfires may be displayed in the specific
work display area 106 as a guideline for enabling the operator to
judge a misfire pattern.
In the above embodiment, the external diagnosing machine 14
acquires data upon the occurrence of a misfire directly from the
vehicle 12 (engine ECU 20). However, the external diagnosing
machine 14 may acquire data indirectly through a relay device upon
the occurrence of a misfire. The relay device may be a wireless
relay unit, which communicates with the engine ECU 20 via a wired
link, and communicates with the external diagnosing machine 14 via
a wireless link. Alternatively, the external diagnosing machine 14
may acquire data upon the occurrence of a misfire through a car
navigation system having a wireless communication function, or a
portable terminal such as a smartphone or the like.
5. Compression Pressure Failure Judgment Test
In the above embodiment, upon cranking the engine 16, both the fuel
supply system (fuel injection valve 42, etc.) and the ignition
system (spark plug 44, etc.) are disabled. Insofar as explosion of
fuel does not occur in the cylinders 36a through 36d, only the fuel
supply system may be disabled upon cranking the engine 16.
In the above embodiment, a compression pressure failure is judged
using angular velocity variations .DELTA..omega. occurring during
the power stroke. However, a compression pressure failure may also
be judged using angular velocity variations .DELTA..omega. that
occur during the compression stroke.
6. Air-Fuel Ratio Failure Diagnostic Test
In the above embodiment, the processor 88 of the external
diagnosing machine 14 switches between the cylinder air-fuel ratios
Ra_n (the fuel injection ratios Rfi_n and the corrective values
Cfi_n) through operation of the engine ECU 20. However, the
processor 88 may directly control the fuel injection valves 42 in
order to switch between the cylinder air-fuel ratios Raf_n (the
fuel injection ratios Rfi_n and the corrective values Cfi_n).
Alternatively, the engine ECU 20 may include the functions of the
external diagnosing machine 14, so that the engine ECU 20 (the
external diagnosing machine 14) can directly control the fuel
injection valves 42 in order to switch between the cylinder
air-fuel ratios Raf_n (the fuel injection ratios Rfi_n and the
corrective values Cfi_n).
In the above embodiment, the corrective values Cfi_n are reduced in
order to reduce the air-fuel ratios Raf_n of the respective
cylinders 36 from the stoichiometric air-fuel ratio to a leaner
air-fuel ratio (FIG. 16). However, the corrective values Cfi_n may
be changed in a stepwise manner from a positive value to a negative
value, so as to change the air-fuel ratios Raf_n in a stepwise
manner from a richer air-fuel ratio to a leaner air-fuel ratio.
Alternatively, the corrective values Cfi_n may be changed in a
stepwise manner from a negative value to a positive value, so as to
change the air-fuel ratios Raf_n in a stepwise manner from a leaner
air-fuel ratio to a richer air-fuel ratio. In such cases, the
corrective values Cfi_n are not necessarily a combination of
.+-.0%, -10%, -20%, -30%, and -40%, but may be changed in other
appropriate ways.
In the above embodiment, the cylinders 36a through 36d, other than
the target cylinder, are controlled according to the basic fuel
injection control process, whereas the air-fuel ratio Raf_n (the
corrective value Cfi_n) of the target cylinder is changed
gradually. However, with respect to cylinders 36a through 36d other
than the target cylinder, the basic fuel injection control process
may be canceled in order to stop injecting and igniting fuel.
7. Other Arrangements
In the above embodiment, a possible faulty region is tracked down
by combining the results of the misfire repeatability test, the
compression pressure failure judgment test, and the air-fuel ratio
failure diagnostic test. However, it is possible to track down a
possible faulty region by conducting either one of the compression
pressure failure judgment test and the air-fuel ratio failure
diagnostic test in addition to the misfire repeatability test.
* * * * *